Several methods are presently used and in combinations thereof which should be considered the state of the art. These consist of using a crane and/or forklift trucks to raise the unassembled vertical member into place, then attach as required, the balance of the structure, raising each piece individually. In other cases, the vertical structure is assembled in the horizontal position at ground or floor level. This method, using the present state of the art, is limited by the following: rigidity and strength of the assembled vertical structure in the horizontal position; balance that will permit controlled raising of the structure; available space to permit assembly at the point of erection; maneuverability of the lifting device and the ability of this device to gain access to the site or location. The problems are particularly acute in the erection of storage racks which have long slender vertical members (several feet in length to 60 or 70 feet long) which have many horizontal members. This type of structure is generally installed in a completed structure or building with no or poor access for a crane. In addition, very little maneuvering room is available particularly near completion when most floor area has been consumed. The lift truck, although smaller and more maneuverable, has great difficulty lifting a load off-center particularly when the mast is extended. This is true because the lift must engage the vertical member column at right angles keeping clear of the horizontal members and above the balance point. This produces a side thrust as the lift truck mast is raised. Lifting from the top of the vertical member would require a forklift truck which has a lifting capacity in excess of the vertical member to be raised. In many cases, lifts of this capacity are rare, very expensive and lack maneuverability. It is also necessary to drive forward as the structure is raised or drag it to the lift.
Regardless of the device used, a number of shortcomings become evident. These include:
1. Access to the immediate erection site. PA0 2. Space to maneuver heavy or large equipment. PA0 3. Space above the installed vertical members. PA0 4. Availability of the exceptionally high lift capacity for lift trucks. PA0 5. Poor structural integrity of the vertical member when lifted from the horizontal position, particularly when preassembled. PA0 6. Difficulty moving an assembled member from the assembly area to a point of erection. PA0 7. Space requirements when assembling in a horizontal position. PA0 8. Positioning at the assembly point so that the work can be performed on both sides or bottom and top. PA0 9. Raising to vertical, a column or structural member, where interference may exist in the ceiling area such as water, steam or electrical lines. This might require raising in a clear area and moving in the raised vertical position to the installation point. PA0 10. Control and placement of an assembled column or a vertical member due to the poor balance resulting from the cantilever type structure. PA0 11. The need for qualified, highly trained equipment operators. PA0 12. Very expensive equipment to either rent or buy and comparably high maintenance and operating costs.
In addition to the many disadvantages as previously outlined, it should be noted that in the erection of pallet storage rack, or selective rack as it is sometimes called, I have never witnessed, nor am I aware of the raising of a fully assembled column with its' horizontal members in place using the present state of the art system or equipment, for many of the reasons stated above to include and particularly the strength of the column and balance of the members assembled.